The present invention relates to broadband communications, and more particularly to methods and apparatus for statistically multiplexing a plurality of services, such as cable or satellite television services, into a combined data stream for transmission to a population of subscriber terminals.
In a typical broadband network, such as a cable television system, satellite television system, subscription network service or the like, subscribers are provided with a broadband communications terminal. A broadband communications terminal contains the electronic equipment that is used, e.g., to connect the subscriber's television, computer and/or other consumer electronic equipment with the broadband network. In the case of a cable or satellite television system, the broadband communications terminal is typically connected to the network through a co-axial wall outlet. Other network connection techniques, such as the use of various standard computer connectors (e.g., universal serial bus “USB” connectors and “Category 5” couplers) are well known in the art.
In the subscription television field, a present day broadband communications terminal is essentially a computer programmed to process the signals from the television network (e.g., cable or satellite) to provide the subscriber with, e.g., cable services. As used hereinafter, the term “cable services” is not intended to be limited to television services received over a cable distribution plant, but can also describe other network services including Internet and data services, which may be delivered over any type of broadband network, including satellite television systems.
Cable services are controlled, e.g., by a cable television company and typically include a number of basic television channels, premium channels which may be provided to subscribers at an additional fee, and pay-per-view events. The broadband communications terminal is programmed to provide these services to the subscriber.
However, the services of the cable company need not be limited to providing television programming. Some cable companies are now offering Internet access and e-mail over the cable network at speeds much faster than are available over conventional telephone lines. It is anticipated in the future that more and more services will be commonly provided over such broadband networks, including video on demand and even basic telephone service. Eventually, each home or office may have a single connection, via the cable network, to all electronic data services. The cable network is also expected to evolve from coaxial cable service to optical fiber service. Currently, optical fiber distribution is in fairly widespread use, except on the “cable drop” to the home. Eventually, fiber is expected to be used in the cable drop, and potentially inside the home itself. The provision of a wholly fiber distribution path is expected to increase the system bandwidth, enabling more services to be provided.
Current broadband networks are limited by the amount of bandwidth they provide, which determines the amount of raw data, and hence the number of services (such as television channels, including movie channels, pay-per-view channels and Internet access) they can carry. One technique for maximizing the data carrying capability of a broadband network is to individually statistically multiplex the services carried over the network. With statistical multiplexing, more bandwidth is provided to services when they need it, and less when they do not. Thus, over time, the bandwidth requirements of all of the services carried is averaged to maintain the total consumed bandwidth within the capabilities of the broadband network. Various statistical multiplexing techniques are well known, as evidenced, for example, in U.S. Pat. No. 5,216,503 to W. Paik, et al. entitled “Statistical Multiplexer for A Multi Channel Image Compression System” and U.S. Pat. No. 6,167,084 to L. Wang et al. entitled “Dynamic Bit Allocation for Statistical Multiplexing of Compressed and Uncompressed Digital Video Signals”,
A satellite transponder, for most communication link budget scenarios, provides transmission capacity in excess of a six MHz cable television channel. Various configurations, such as the split multiplex mode and the recently introduced “Megapipe” configuration (promoted by the Home Box Office (HBO®) television network for a high bandwidth data pipe) permit a subscription television multiple system operator (MSO) to select a subset of satellite feeds to map onto a cable television plant. Devices exist to facilitate this selection/repackaging at the cable television headend at various costs and complexities. Many of these techniques, such as Megapipe, use fixed bit-rate (constant bit rate—CBR) groups of services for predetermined configurations.
As an example of a satellite configuration, a satellite/cable television service programmer may have “East” and “West” time zone feeds. While some MSOs may take both East and West in a given system, capacity-constrained systems may only be able to use the time zone feed specific to their region. Since the satellite capacity may permit carriage of both East and West simultaneously, perhaps along with “non-time-specific feeds”, there still needs to be a method to compress the East, West and non-time-zone feeds while respecting the MSOs ability to select the feed groupings for a given system data rate. The system data rate is typically set by the modulation format used, for example, Quadrature Amplitude Modulation (QAM). Currently, the communication of such feeds is provided using groups of CBR channels. Unfortunately, the CBR groups eliminate some of the compression efficiencies that are obtained by using statistical multiplexing in the encoder.
It would be advantageous to provide a statistical multiplexing method and apparatus for maintaining compression efficiency among different groupings of service feeds, in a manner that allows MSOs to select particular feed groupings. It would be still further advantageous if both overlapping and non-overlapping groups could be accommodated. The present invention provides a multi-group statistical multiplexer and methods having the aforementioned and other advantages.